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vhea — Vertical Header Table

8/16/2018

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The vertical header table (tag name: 'vhea') contains information needed for vertical fonts. The glyphs of vertical fonts are written either top to bottom or bottom to top. This table contains information that is general to the font as a whole. Information that pertains to specific glyphs is given in the vertical metrics table (tag name: 'vmtx') described separately. The formats of these tables are similar to those for horizontal metrics ('hhea' and 'hmtx').

Data in the vertical header table must be consistent with data that appears in the vertical metrics table. The advance height and top sidebearing values in the vertical metrics table must correspond with the maximum advance height and minimum bottom sidebearing values in the vertical header table.

Table Format

The difference between version 1.0 and version 1.1 is the name and definition of the following fields:

ascender becomes vertTypoAscender

descender becomes vertTypoDescender

lineGap becomes vertTypoLineGap

Version 1.0 of the vertical header table format is as follows:

Version 1.0

Type

Name

Description

Fixed

version

Version number of the vertical header table; 0x00010000 for version 1.0

int16

ascent

Distance in FUnits from the centerline to the previous line’s descent.

int16

descent

Distance in FUnits from the centerline to the next line’s ascent.

int16

lineGap

Reserved; set to 0

int16

advanceHeightMax

The maximum advance height measurement -in FUnits found in the font. This value must be consistent with the entries in the vertical metrics table.

int16

minTopSideBearing

The minimum top sidebearing measurement found in the font, in FUnits. This value must be consistent with the entries in the vertical metrics table.

int16

minBottomSideBearing

The minimum bottom sidebearing measurement found in the font, in FUnits. This value must be consistent with the entries in the vertical metrics table.

int16

yMaxExtent

Defined as yMaxExtent = max(tsb + (yMax - yMin)).

int16

caretSlopeRise

The value of the caretSlopeRise field divided by the value of the caretSlopeRun Field determines the slope of the caret. A value of 0 for the rise and a value of 1 for the run specifies a horizontal caret. A value of 1 for the rise and a value of 0 for the run specifies a vertical caret. Intermediate values are desirable for fonts whose glyphs are oblique or italic. For a vertical font, a horizontal caret is best.

int16

caretSlopeRun

See the caretSlopeRise field. Value=1 for nonslanted vertical fonts.

int16

caretOffset

The amount by which the highlight on a slanted glyph needs to be shifted away from the glyph in order to produce the best appearance. Set value equal to 0 for nonslanted fonts.

int16

reserved

Set to 0.

int16

reserved

Set to 0.

int16

reserved

Set to 0.

int16

reserved

Set to 0.

int16

metricDataFormat

Set to 0.

uint16

numOfLongVerMetrics

Number of advance heights in the vertical metrics table.

Version 1.1 of the vertical header table format is as follows:

Version 1.1

Type

Name

Description

Fixed

version

Version number of the vertical header table; 0x00011000 for version 1.1Note the representation of a non-zero fractional part, in Fixed numbers.

int16

vertTypoAscender

The vertical typographic ascender for this font. It is the distance in FUnits from the ideographic em-box center baseline for the vertical axis to the right edge of the ideographic em-box.

It is usually set to (head.unitsPerEm)/2. For example, a font with an em of 1000 fUnits will set this field to 500. See the Baseline tags section of the OpenType Layout Tag Registry for a description of the ideographic em-box.

int16

vertTypoDescender

The vertical typographic descender for this font. It is the distance in FUnits from the ideographic em-box center baseline for the vertical axis to the left edge of the ideographic em-box.

It is usually set to (head.unitsPerEm)/2. For example, a font with an em of 1000 fUnits will set this field to -500.

int16

vertTypoLineGap

The vertical typographic gap for this font. An application can determine the recommended line spacing for single spaced vertical text for an OpenType font by the following expression: ideo embox width + vhea.vertTypoLineGap

int16

advanceHeightMax

The maximum advance height measurement -in FUnits found in the font. This value must be consistent with the entries in the vertical metrics table.

int16

minTopSideBearing

The minimum top sidebearing measurement found in the font, in FUnits. This value must be consistent with the entries in the vertical metrics table.

int16

minBottomSideBearing

The minimum bottom sidebearing measurement found in the font, in FUnits. This value must be consistent with the entries in the vertical metrics table.

int16

yMaxExtent

Defined as yMaxExtent = max(tsb + (yMax - yMin)).

int16

caretSlopeRise

The value of the caretSlopeRise field divided by the value of the caretSlopeRun Field determines the slope of the caret. A value of 0 for the rise and a value of 1 for the run specifies a horizontal caret. A value of 1 for the rise and a value of 0 for the run specifies a vertical caret. Intermediate values are desirable for fonts whose glyphs are oblique or italic. For a vertical font, a horizontal caret is best.

int16

caretSlopeRun

See the caretSlopeRise field. Value=1 for nonslanted vertical fonts.

int16

caretOffset

The amount by which the highlight on a slanted glyph needs to be shifted away from the glyph in order to produce the best appearance. Set value equal to 0 for nonslanted fonts.

int16

reserved

Set to 0.

int16

reserved

Set to 0.

int16

reserved

Set to 0.

int16

reserved

Set to 0.

int16

metricDataFormat

Set to 0.

uint16

numOfLongVerMetrics

Number of advance heights in the vertical metrics table.

'vhea' Table and OpenType Font Variations

In a variable font, various font-metric values within the 'vhea' table may need to be adjusted for different variation instances. Variation data for 'vhea' entries can be provided in the metrics variations (MVAR) table. Different 'post' entries are associated with particular variation data in the MVAR table using value tags, as follows: